This invention relates to a solid state breakerless ignition module which may be supplied as a retrofit package enabling the replacement of the more conventional mechanically actuated breaker points.
To control the generation of a spark in an ignition system, many such systems utilized a pair of breaker points which were moved in synchronism with the combustion cycle within the engine by a cam. These breaker points require manual setting to achieve the proper ignition timing and typically have a relatively limited life because of the wearing down of a rubbing block moved by the cam. In addition, the electrical contacts of the breaker points are subject to pitting and electrical corrosion due to the electrical arcing that often occurs thereacross further limiting its useful life.
Further, the packaging of an ignition system especially for a small engine such as a chain saw, lawn mower, or the like, is especially critical since available space is at a premium. Such is not the case for ignition systems for larger automotive engines. The present invention is directed to a retrofit ignition module which can be used to convert the conventional mechanical breaker ignition system into a solid state, breakerless ignition system and as such the module and related circuitry must be sufficiently compact to be packaged and received within the exsisting confines of the ignition system. One such ignition system is illustrated in U.S. Pat. No. 4,270,509 which uses separate biasing coil wound about an additional ferromagnetic core which is thereafter fitted to the main core of the magneto. The present invention avoids the complicated mounting requirements of the above system and is not sensitive to air gap variations of the additional core.
It is a general object of the present invention to provide a retrofit ignition module for a mechanical breaker ignition system that can be quickly and easily installed as a replacement for a mechanical points and condensor. It is a further object of the invention to provide such ignition module which is compact and able to fit within the existing space requirements of the small engine ignition system.
Accordingly, the invention comprises; a retrofit ignition module for an ignition system having a generally U-shaped core, including a crossbar and two substantially parallel extending legs. The ignition system further includes an ignition coil wound about the crossbar including a primary and a secondary coil winding. The ignition module comprises a user replaceable drive winding adapted to be circumferentially positioned about one of the legs of the core for generating a first induced control signal in response to a varying flux field produced by the movement of the magnet across the end faces of the legs. The ignition module further includes a circuit cantilevered from the drive winding and positioned within the main core between the drive winding and the ignition coil. The control circuit being responsive to the induced control signal and connected in circuit between the drive winding and the primary winding and operable to control the flow of current through the primary winding.
Many other objects, features and purposes of the invention will be clear from the following detailed description of the drawings.